Lung scintigraphy in postpneumonectomy dyspnea due to a right-to-left shunt

We report the case of a 50-yr-old man who experienced exertional dyspnea 5 mo after a left pneumonectomy for carcinoma. As the clinical features pointed toward a pulmonary embolism, we performed a ventilation plus perfusion radionuclide lung scan. It showed no evidence of pulmonary embolism, but it did show a systemic uptake of the isotope, suggesting a right-to-left shunt that was confirmed by contrast echocardiography, which revealed an atrial septal defect. Right-to-left shunts after pneumonectomy have already been reported and can be diagnosed by lung scintigraphy. Usually, a patent foramen ovale is encountered, but the underlying physiopathology remains under discussion. Clinically, right-to-left shunts are often related to platypnea-orthodeoxia.